During data transmission in a connectionless network, data can be sent in the form of data packets from a terminal to a destination or a receiver, the network or switching nodes (generally “core routers” or edge routers) located on the transmission path receiving, together with the data packet, information as to how the data are to be forwarded. If, on the other hand, before data are sent by a terminal, a path through the network to the receiver first has to be set up or signalled, this is what is known as a connection-oriented data transmission. In this case, the network nodes (generally “switches”) are provided beforehand by measuring packets with the necessary connection information in order to then correctly forward the sent data.
The transition between two networks or sub-networks, such as, for example, the transition between a core network and a connection network, is generally called an edge in networks. While what are known as inner routers (IR routers) or core routers are used as switching nodes in the core network, what are known as edge routers, which take on the switching function between the core network and the connection region and are therefore the broadband access of a network connection on what is known as the last mile, are used at net transitions. In an autonomous system of a network integration, at least one edge router is set up, for example, as what is known as an exterior gateway, which connects the autonomous system to another autonomous system. Such edge routers are connected to the switching nodes (core routers) in the core network and transfer the data packets between the core network and the connection network.
In MPLS routing, what are known as tunnels or MPLS paths are realised in the network to transmit data packets. For this purpose, the destination of a packet is determined with the aid of its received destination address information in order to send the packet on the corresponding MPLS path. This may be an IP-address, MPLS information, Ethernet information or other destination information. An MPLS (network) edge router or switching node determines, with the aid of this address information, an address stack or label stack for the relevant data packet, which it adds to the data packet. The MPLS path, which the packet takes via the edge router(s) on the path to the destination, is thus determined.
On the path to the destination, the upper label of the address stack or label stack is exchanged at each router of the valid transport level. At the destination edge router or at the router or switching node located before this, the upper label or the upper address of the label stack or the address stack is then removed. The destination edge router forwards the data packet as an IP packet or evaluates a “virtual connection label” and then determines the next step. In the process, the destination edge router removes the “virtual connection label” and sends the packet to a local interface, which is identified by the “virtual connection label”. Alternatively, the destination edge router replaces the “virtual connection label” and supplements a further transport label on the data packet.
In order to send back an IP measuring packet to a sender or to loop it, an IP-echo request/reply function has to be used, also known as a “ping” (standards: RFC 792 for IPv4 and RFC 2463 for IPv6). A comparable function was also standardised for MPLS, for example an MPLS- or IP-echo request/reply function (MPLS ping, standard RFC 4379). Measurements can be carried out at each edge router with measuring apparatuses of their own between two measuring points, or measuring loops as line pieces between physical ports of an edge router or as a continuity check as in IEEE 802.1 ag or Y. 1731 being a further solution possibility. Conventional solutions, for example according to the standard RFC 5085, loop data packets back at the level of a virtual connection. However, the conventional standards without exception require special configurations or software at the two ends of a measuring connection and therefore special configurations or software at at least two edge routers. In some of the conventional solutions, the forwarding level is left and the measuring packet is processed by the software of the edge router, which may, however, falsify the measurement. Other solutions assume a connection-oriented path guidance, in which an MPLS path has to be present in the two directions at each MPLS router.